OK- so maybe that's not the best thread title, but anyway what i'm wanting to do is use some foam to build an aux tank, then coat that with fiberglass. My concern is the fiberglass not holding up well in dual-sport conditions or if the bike gets dropped. Is there some sort of flexible fiberglass option? I could do kevlar or carbon fiber, but that's pretty expensive. Ideally, I'd like to make the tank out of plastic, but this is more of a 1-off project, and that would get pretty expensive to have a mold made for 1 tank.

At the moment, I'm thinking about using that green floral foam, since it's pretty easy to shape, Styrofoam would work too, but I think it's a bit harder to shape smoothly. Tends to break off in chunks, although that could be because I was using the wrong type of foam.

i like useing construction foam... you know-the pink or blue stuff you see at homedepo, lowes, etc...cuts easyly with a knife or a "hot wire", it shapes with common sand paper. if you're thinking of flat sided shapes,( and a lot of curved shapes as well) there's easyer ways to make this quickly take a look at aircraft spruce and speciality they have a lot of core foams, as well as the fixings for about any fiberglass project

OK- so maybe that's not the best thread title, but anyway what i'm wanting to do is use some foam to build an aux tank, then coat that with fiberglass. My concern is the fiberglass not holding up well in dual-sport conditions or if the bike gets dropped. Is there some sort of flexible fiberglass option? I could do kevlar or carbon fiber, but that's pretty expensive. Ideally, I'd like to make the tank out of plastic, but this is more of a 1-off project, and that would get pretty expensive to have a mold made for 1 tank.

At the moment, I'm thinking about using that green floral foam, since it's pretty easy to shape, Styrofoam would work too, but I think it's a bit harder to shape smoothly. Tends to break off in chunks, although that could be because I was using the wrong type of foam.

Thoughts? Comments?

G

If you are thinking plastic, why not natural clay. It is cheap, easy to form and easy to clean up.

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Both good suggestions, but what I'm more curious about is the material for the final product- as I mentioned, I have concerns about the durability of fiberglass. Anyone have any thoughts on an alternative? Ideally some sort of plastic, but I can't really think of anything that could be done at home, without special tooling.

Fiberglass will be fine, maybe use a vinelester resin or an epoxy if you want to be certain. Construction styrefoam cut with a hot wire will do a nice quick job. The only problem I see is getting rid of the foam from inside the tank, melting it out with gas is a very messy affair.

I wouldn't want any flex at all in a tank that holds liquids, if it flexes at all on a regular basis it will crack and leak over time at some point.

Anyway, one way to lay up your tank is to carve the foam and then cover the tank completely. When the glass has cured cut an access hole in the top and clean out the foam, then glass your filler spout into the opening.

GM- that's exactly what I was thinking- shape the form, lay up the fiberglass, then cut a hole in it to remove the foam inside. What I'm leaning towards at the moment is using a flush mount filler cap like this:
mounted to a flat spot on the top of the tank. I haven't been able to figure out how big that piece is, but I think if it's 4" diameter or less, I should be ok. Ideally, I could find something off a motorcycle, but unless I get lucky at a salvage yard, I have to take what I can find.

You can try calling 2 aircraft salvage yards- Global Aircraft Parts in Alberta, CA at 800-561-6448, and O.K. AIRCRAFT PARTS in Hollister CA at 831-636-9036, if either of those places are close to you. Tell them you are looking for a flush mount fuel filler.

why even remove the foam? with propper core foam mat'l, you leave the foam core intact..it adds strength and ridgitness. it can be made into rounded shapes, but does take a bit of work....but flat sided projects, it's the fastest way to turn out a project.

Flexablity ...
It is the glue (resin) in the fiberglass that makes it ridgid. Same goes for kevlar. I'd not use carbon fiber that close to my person - see the photos of carbon fiber arrows that have shattered into the bow persons arm .. not nice! (use google)

In the '80s some trail bikes had fiberglass tanks - the things were 1/4inch thick and could take a fair pounding! I'd suggest you make your tank nice an thick too .. that way it should survive falling on to a rock.

At the moment, I'm thinking about using that green floral foam, since it's pretty easy to shape, Styrofoam would work too, but I think it's a bit harder to shape smoothly. Tends to break off in chunks, although that could be because I was using the wrong type of foam.

Thoughts? Comments?

G

The green floral foam won't dissolve with gasoline. I'm sure there IS some solvent that will take it out, but the only time I use it is when I want to use polyester resin and leave the foam in place. BTW, if you want to use a polystyrene foam (like expanded bead foam, or the blue or pink closed cell foams) the Polyester resin will melt it. Either use epoxy resin, or make very sure you have completely sealed the foam with something resistant to the resin.
I've built tanks with glass, but even well sealed, they don't last forever. I'd be more inclined to beat one out of aluminum, and live with the inevitable dents.

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I've built tanks with glass, but even well sealed, they don't last forever. I'd be more inclined to beat one out of aluminum, and live with the inevitable dents.

OK- I'll have to explore foam options.
I thought (briefly) about going with AL, but I have absolutely no experience, and no tools. I am willing to try to model a tank out of cardboard, then try to copy it in metal, but I'm afraid that the cost may be prohibitive, as I don't have a welder. If I could come up with something that didn't have a bunch of complex bends and curves, I could probably make a go of it though. I know if I went with metal, I'd want something easy to fab, whereas with fiberglass, I wouldn't have to worry too much about a complex shape- just lay on the cloth and add resin. When I get my exhaust back together, I'll go from there.

OK- I'll have to explore foam options.
I thought (briefly) about going with AL, but I have absolutely no experience, and no tools. I am willing to try to model a tank out of cardboard, then try to copy it in metal, but I'm afraid that the cost may be prohibitive, as I don't have a welder. If I could come up with something that didn't have a bunch of complex bends and curves, I could probably make a go of it though. I know if I went with metal, I'd want something easy to fab, whereas with fiberglass, I wouldn't have to worry too much about a complex shape- just lay on the cloth and add resin. When I get my exhaust back together, I'll go from there.

G

You might be surprised how cheaply you can get it welded if you have the pieces shaped to suit. Many local machine shops and metal shops will do it in their off time for a few bucks. Just make sure the welds are leak proof before completing the project. IMHO metal will be cheaper and stronger than fiberglass.

you should check out my posts ,i made auxilery fuel tanks for my saddlebags out of metal and made a fes oversized gas tanks for my xr 650l.used a 110 volt mig welder.heres a pic of my last 6 gallon gas tank made of metal for my xr.